Cerebral blood flow in transient hypothyroidism after thyroidectomy: Arterial spin labeling magnetic resonance study

OBJECTIVE: Our purpose was to apply arterial spin labeling (ASL) magnetic resonance imaging (MRI) to characterize regional cerebral blood flow (rCBF: the CBF values at each voxel / the subject's mean global flow) in patients with transient hypothyroidism after thyroidectomy. METHODS: Our study included 27 patients who had undergone total thyroidectomy due to thyroid cancer and pre-I-131 therapy and 24 controls. Patients were evaluated at two points in time: before and after thyroxine replacement. The assessments for the patients and controls consisted of evaluation of ASL of the brain and the severity of depression using 21-question Beck Depression Inventory (BDI). The assessments for the patients also included thyroid hormone lebel. We performed the comparison of rCBF between patients and controls, and investigated the association between rCBF in hypothyroid patients and thyroid hormone level and BDI score. RESULTS: Hypothyroid patients showed a significantly lower rCBF in the cerebellum, the left thalamus and some regions, and showed a significantly higher rCBF in the bilateral frontal gyri and some regions. After thyroxine replacement, patients showed a significantly lower rCBF mostly in the right frontal lobe, and showed a significantly higher rCBF in the left frontal and parietal lobes, although the degree of rCBF changes was lower after thyroxine replacement. In the hypothyroid patients, significant positive relationships were found between free T3 and the rCBF (p<0.05 corrected for FDR). CONCLUSIONS: This study revealed alterations of rCBF in patients with transient hypothyroidism. ASL is helpful for understanding of the effects of hypothyroidism on the brain.